1. Field of the Invention
The present invention relates to a method of fabricating a stamper, and more particularly, to a method capable of forming a plurality of patterns having microlens surfaces and large dimensions, or a plurality of patterns with different heights onto a stamper. The above stamper can be utilized to fabricate a light guide plate.
2. Description of the Prior Art
A light guide plate (LGP) is an important element of an LCD. The light guide plate functions to reflect the light source generated by a back light module toward each pixel region so that the LCD has a brilliant and uniform brightness. In order to improve the light usage, the light guide plate normally includes a plurality of patterns thereon so as to transform point light source into a planar light source. The size or shape of the patterns, however, varies according to different optic designs of the back light module or different allocations of the fluorescent tubes.
Since the light guide plate is substantially composed of plastic materials, it is generally fabricated by injection molding technology. At present, the insert mold is often combined with a stamper that has patterns thereon to form the light guide plate. Please refer to FIG. 1 to FIG. 3. FIG. 1 to FIG. 3 are schematic diagrams illustrating a conventional method of forming a stamper having a plurality of microlens patterns thereon. As shown in FIG. 1, a substrate 10 is provided, and a photo resist layer 20 is then coated onto the substrate 10. As shown in FIG. 2, an exposing and developing process is performed by a photo mask (not shown) to remove parts of the photo resist layer 12 so as to form a plurality of photo resist patterns (such as 14A and 14B).
As shown in FIG. 3, a flow process is then performed in order to make each photo resist pattern have a smooth microlens surface. In the flow process, the temperature of the photo resist patterns is raised over its glass transition temperature, and three kinds of tensions, which are tension between photo resist and atmosphere (γP-A), tension between photo resist and substrate (γp-s), and tension between substrate and atmosphere are acted on the each photo resist pattern(γs-A). While these three tensions reach to an equivalent state, a photo resist pattern having a microlens surface (such as 14A) will be formed.
As described, the dimensions of the microlens patterns change with different designs of the light guide plate. As long as the microlens patterns to be formed have large dimensions (for example large radius at the bottom of the photo resist pattern), the contact angle of the photo resist pattern is not capable of supporting the microlens surface. Consequently, the photo resist pattern will collapse (as 14B shown in FIG. 3). The conventional method suffers from the collapse of the photo resist patterns.
In addition, in order to improve the light usage (particularly for a large size light guide plate), many light guide plates require the microlens patterns that have different heights or depths. These requirements obviously cannot be achieved by the conventional method. Therefore, the remedy so far is to form the stamper that has a plurality of microlens patterns having different heights or depths mechanically after the stamper is fabricated. Unfortunately, the mechanical way is time-consuming. What is worse is that the microlens patterns become rough after the mechanical treatment. The stamper with rough microlens patterns cannot be used to fabricate a high quality light guide plate.
In view of this shortcoming, developing a new method of forming a stamper that has smooth microlens patterns is important for fabricating a light guide plate that have microlens patterns with different heights or depths.